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By means of the Interaction Region Indicator (IRI) and Quantum Theory of Atoms in Molecules (QTAIM), the influence exerted by NH 2 (amino) and CN (cyano) as electron donor and electron acceptor substituent groups, respectively, located at para –positions of axial and equatorial pyridine rings of derivatized complexes coming from the [(PY 5 Me 2)MoO]+ complex during the hydrogen molecular release in the gas phase was analyzed. In any case, a H–H covalent bond is forming at the transition state, with a strengthening of the electron density of 5.5% when the substituent group involved is NH 2 at the para –position of the axial pyridine ring. However, there was no difference between NH 2 and CN when these substituent groups are located at the para –positions of the equatorial pyridine rings. The topological properties of electron densities from the QTAIM are not perturbed by the electron donor and electron acceptor nature of the substituents, even when these substituent groups are located at the axial or equatorial pyridine rings of the Mo–based complex. [Display omitted] • Combined QTAIM/IRI Topological Analysis for quantifying the capability to release molecular hydrogen. • Evaluating the effect of Axial/Equatorial positions of NH 2 and CN substituents on the molecular hydrogen release. • A strong H–H polar covalent interaction is clearly revealed. • The molecular hydrogen release occurs without mattering the substituent group's nature and its axial or equatorial location. • The link between topological analysis and rate constants is not clear nor evident. [ABSTRACT FROM AUTHOR]

The local chemical reactivity of FOX-7 (1,1-diamino-2,2-nitroethylene, also known as DADNE from DiAminoDiNitroEthylene) was elucidated through a quantitative study of the electrostatic potential on the molecular surface, topological analysis based on Bader's theory, and the EDA-NOCV method. Unlike (O 2 N) 2 C C(NH 2) H 2 N ⋯ Cp 2 M CH 3 + complexes, which exhibit both σ -donor and π -acceptor features, the situation is different concerning the (H 2 N) 2 C C(NO 2) (O)N O ⋯ Cp 2 M CH 3 + complexes, where both charge transfers correspond to the σ -donation. The two charge transfers reinforce each other, resulting in increased stability for (H 2 N) 2 C C(NO 2) (O)N O ⋯ Cp 2 M CH 3 +. This seems to strengthen the (H 2 N) 2 C C(NO 2) (O)N O ⋯ M= { Ti,Zr,Hf } bond, which may explain the high stability of (H 2 N) 2 C C(NO 2) (O)N O ⋯ Cp 2 M CH 3 + compared to (O 2 N) 2 C C(NH 2)-H 2 N ⋯ Cp 2 M CH 3 +. Results from topological analysis revealed that the decreased sensitivity to decomposition of C NO 2 bonds depends on the chemical nature of the interacting metal, and the best achievements are obtained for the Hf-based complex. Our results demonstrate that the interaction of M = { Ti,Zr,Hf } with C NO 2 is more favourable than that with C NH 2 , this specific action on the trigger bond may support the use of Metallocene Methyl Cations (MMC) as possible neutralisers. [Display omitted] • Effect of electron-donating/accepting groups on the C NO 2 trigger bond is examined. • Strong sigma-electron-donating achieves good overlap with the metal orbital. • Sensitivity of C NO 2 depends on the chemical nature of the interacting metal. • Oxygen...Metal interaction rules the complex formation when NO 2 interacts with MMC. • MMC acts specifically on trigger bonds. [ABSTRACT FROM AUTHOR]

This paper outlines the role of intermolecular interactions involving group 4 transition metals in stabilising the N–NO 2 trigger bonds. Minimising sensitivity is the foremost priority in designing energetic compounds. A quantitative analysis with Molecular Electrostatic Potential (MEP) evidenced anomalies arising from the marked depletion of negative charge distribution of RDX and HMX. The Energy Decomposition Analysis with Natural Orbitals for Chemical Valence (EDA-NOCV) results reveal that the electrostatic and orbital contributions are the dominant factors driving the assembly of the M = { Ti , Zr , Hf } -based complexes. Sensitivity of the N–NO 2 trigger bonds is investigated by using the Quantum Theory of Atoms in Molecules (QTAIM). The QTAIM topological analysis showed that the O ⋯ M = { Ti , Zr , Hf } interaction strengthens these trigger bonds, revealing an increased stability to decomposition. This effect is more marked in the Hf- and Zr-based complexes. Finally, the results based on Interaction Indicator Region (IRI) are fully consistent with those generated from QTAIM analysis. [Display omitted] • RDX and HMX can favourably interact with group IVA metallocene methyl cations, Cp 2 MCH 3 +. • This interaction is driven through an O ⋯ M = { Ti , Zr , Hf } interaction leading to RDX/HMX-Cp 2 MCH 3 + complexes. • MEP, EDA-NOCV, QTAIM, and IRI were employed for the first time in this context. • Electrostatic contribution is dominant, leading to stabilising the formed complexes. • The stabilisation suggests that metallocene methyl cations can be candidates to be used as neutralisers for energetic materials. [ABSTRACT FROM AUTHOR]

The electron density depletion associated with π -hole at the ring center typical of energetic compounds was clearly revealed by the molecular electrostatic potential (ESP). In addition, the spatial arrangement of NO 2 groups appears to affect the ESP value in the ring center, and therefore sensitivity to detonation. Indeed, for monocyclic nitrobenzene compounds with the same number of NO 2 groups, the ESP value in the ring center decreases as the NO 2 groups are more closely spaced. As expected, the central rings become less aromatic as NO 2 groups are added. The MCI, PDI, PLR, NICS z z (1), FLU indices are all strongly correlated with the ESP values observed in the ring center of the set of nitrobenzenes. Aromaticity indices based on electron delocalization criteria appear to be very sensitive to small variations in aromaticity. Among magnetic-based indices, only NICS z z (1) is capable to predict small changes in aromaticity. The PLR index derived from conceptual DFT is quite relevant for predicting small variations in aromaticity. According to our results, the most suitable aromaticity index is not based on a single criterion, and that selecting it is more subtle. Therefore, it is important to combine information from several criteria to obtain a more complete description of the aromaticity of the studied compounds. [Display omitted] • Spatial arrangements of NO 2 groups affect the ESP value at the ring center. • ESP value at the ring center decreases as the NO 2 groups are closely spaced. • Central rings become less aromatic as NO 2 groups are added. • NICS z z (1) is capable of properly predicting small changes in aromaticity. • Delocalization-based indices are sensitive to slight changes in aromaticity. [ABSTRACT FROM AUTHOR]